A virtual machine is a virtualized copy of a computer system, with virtual hardware that includes a disk controller, a network card, and other similar devices. Frequently, running within the virtual machine is a full operating system, such as Linux or Microsoft Windows. These virtual machines run on a physical host server that includes a hypervisor, which abstracts the physical hardware of the host server allowing the virtual machine to see virtual hardware regardless of what the underlying hardware actually comprises.
Typically, virtual machines suffer from limitations on the number of Small Computer System Interface (SCSI) drives that can be attached to the virtual machines. This limitation is incurred by the hypervisor, which has limits on the number of buses that can be presented to the virtual machine. As a result, a virtual machine is limited to the number of drives that can be communicated over the predefined buses.